Joints often undergo degenerative changes due to a variety of reasons. When joint degeneration becomes advanced or irreversible, it may become necessary to replace the natural joint with a prosthetic joint. Artificial implants, including hip joints, shoulder joints, and knee joints are widely used in orthopedic surgery. Specifically, hip joint prostheses are common. The human hip joint acts mechanically as a ball and socket joint, wherein the ball-shaped head of the femur is positioned within the socket-shaped acetabulum of the pelvis. Various degenerative diseases and injuries may require replacement of all or a portion of a hip using synthetic materials, typically metals, ceramics, or plastics.
It may become necessary to conduct a second or subsequent surgery in order to replace a prosthetic joint with a (often larger) replacement joint. Such surgeries, known as “revision” surgeries, often occur due to further degeneration of bone or advancement of a degenerative disease, requiring removal of further bone and replacement of the removed, diseased bone with a larger or enhanced prosthetic joint, often referred to as a revision prosthesis. For example, bone is often lost around the rim of the acetabulum, and this may provide less rim coverage to securely place an acetabular cup.
In cases where the patient's bone around an implant is compromised, it may be necessary to utilize an augment to add additional support. For example, an acetabular augment may be placed to fill in a defect cavity around the acetabular shell to help support the loads transmitted to the shell. As part of the surgical technique, the surgeon may place both the shell and augment within the patient in order to ensure a proper fit before fastening the two components together to prevent motion between them. However, fastening the two components may be difficult, particularly when using bone cement, if the two components are congruent. Inadequate cementing between the components may cause them to separate after implantation, possibly causing particle generation and leading ultimately to revision.
In current augment designs no provision is typically given to assist with cement application. Therefore, surgeons apply the cement ad hoc (e.g., along the edges of the augment similar to a caulking bead) before fully assembling the components together or forgo the use of cement altogether. This leads to inconsistent and sometimes undesirable results with techniques that are not easily replicated.